Fuel dispensing systems used at retail gas stations typically include an underground tank containing gasoline, diesel fuel or other liquid fuels, an above ground dispensing unit terminating in a nozzle adapted to supply the fuel to a motor vehicle, and a piping system interconnecting the underground tank and dispensing unit. While infrequent, vehicles can collide with the dispensing unit, causing the dispensing unit to be displaced. It is also possible for the unit to be displaced due to certain environmental conditions. In either event, a fuel pipe or conduit may rupture, causing fuel to be spilled and creating a potentially hazardous condition, unless preventive measures are taken.
A variety of emergency fuel shutoff valves are known in the art that have been developed in response to the foregoing potential problem. Known valves of this type include those having upper and lower housings releasably connected to one another, with the lower housing rigidly mounted. For instance, the lower housing can be mounted within a sump located beneath a concrete pedestal supporting the dispensing unit using, for example, a mounting bar as is known in the art. The lower housing is operably connected to the underground tank via underground conduits, while the upper housing is operably connected to the fuel dispensing unit.
A weakened portion, such as a circumferential groove, formed in the upper housing provides a planned failure site so that a first portion of the valve can separate from a second portion of the valve when one of the first or second portions is subjected to a predetermined load. Such a separation of valve portions causes a valve element in the lower housing to move from a releasably latched open position to a closed position, shutting off the flow of fuel from the underground tank. Shutoff valves of this type may also include a check valve in the upper housing that closes under the action of a biasing member when the valve portions separate. The check valve may reduce or prevent the backflow of fuel from the dispensing unit.
Emergency shutoff valves of the foregoing type have been successfully used in fuel dispensing systems, but they can exhibit certain disadvantages. For instance, it is possible even though highly unlikely for the dispensing unit to be subjected with a load or force that is not sufficient for the first portion of the shutoff valve to be separated from the second portion of the valve, but is sufficient to compromise the structural integrity of the valve housing. In other words, a load may in a very unusual situation crack the valve housing along the groove without completely separating the valve portions on either side of the groove. In this event, the valve element in the lower housing may not close, which may permit fuel to escape from the housing through the cracked or otherwise damaged weakened portion of the valve, resulting in undesirable spillage of fuel to the environment.
It is therefore desirable to provide an emergency shutoff valve for use in fuel dispensing systems that overcomes the disadvantages associated with known emergency shutoff valves.